BILE SECRETION
Normal adult produces 250 to 1100 ml.
bile per day.
*
Vagal stimulation increase secretion
*
Stimulation of splanchnic nerves results in decreased bile
flow
*
Bile salts are
very effective choleretics
(stimulate
secretion).
Biliary Secretion
Lobules of the hepatocytes are the source of hepatic
bile secretion. Blood flow to the hepatocytes comes from brahches of both the
portal vein and the hepatic artery. Blood from the portal vein flows through
sinusoids past the hepatocyte to the central vein where it drains into the
hepatic veins and inferior vena cava. Only one layer of hepatocutes separates
the sinusoids.
Bile is a solution of both organic and inorganic
compounds.
The hepatocyte secretes two primary bile acids,
cholic acid and chenodeoxycholic acid. These are synthesized in the hepatocyte
from cholesterol and recycled through the enterohepatic circulation to conserve
bile salts. Primary bile acids, are converted to secondary bile acid
(deoxycholic acid and lithocholic acid) when in contact with bacteria in the
GIT
Purpose of secretion of bile acids is to allow for
the formation of micelles. Micelles are formed and the, bile acid form the
outer layer with the fats in the centre so that they will be more soluble in
the aqueous medium. The emulsion then move down the gastrointestinal tract and
allow lipids that are ingested to freely move in and out of the micelles so
that they can be presented to the enterocytes for absorption.
The pigment of bile give it its color, is bilirubin.
Bilirubin is derived from the degradation of hemoglobin in the
reticuloendothelial system. Because bilirubin itself is not soluble. It is
conjugated primarily with glucuronide and occasionally with sulfate.
Circulating bilirubin is bound to albumen from which it dissociates at the
hepatocyte on the portal venous membrane. It enters the bile canaliculus as
bilirubin diglucuronide.
The bile acids, are synthesized or reused by the
hepatocutes as they are presented as conjugated and unconjugated bile acids
from the portal circulation. The liver produces approximately 500 to 1000 ml of
bile per day.
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